Removing metals with a 2-pyrrolidone-alcohol mixture



United States Patent Otlice 3,052,627 Patented Sept. 4, 1962 3,052,627 REMOVING METALS WITH A Z-PYRRGLIDQNE- ALCUHOL MIXTURE Bernard J. Lerner, Pittsburgh, Pa, assignor to Gulf Research & Development Company, Pittsburgh, Pa, a corporation of Delaware No Drawing. Filed May 22, 1959, Ser. No. 814,950 3 Claims. (Cl. 208251) This invention relates to improved procedure for preparing distillate fractions of crude petroleum which are relatively free of metalloporphyrin complexes.

It is well known that metalloporphyrin complexes such as nickel, vanadium and/or copper porphyrin complexes occur in crude oils. These complexes have a deleterious eifect during the use of the petroleum and its fractions. For instance, gas oils prepared from crudes containing relatively large amounts of these complexes cause rapid deactivation of the cracking catalyst when such gas oils are cracked thereon. Also fuel oils prepared from ciudes containing metalloporphyrin complexes cause a decrease in life of the heating equipment such as boilers in which such fuel oils are burned. It has been proposed to remove these metalloporphyrin complexes by various methods. For instance, it is known that they can be removed by extraction with certain solvents such as furfural. It is also known that these complexes can be more or less completely removed by hydrogenation under high temperature and pressure in the presence of a catalyst. However these procedures are not entirely satisfactory. The hydrogenation operation is short-lived because the metalloporphyrin complexes in many cases have a harmful effect on the hydrogenation catalyst. Also, this type of process is rather expensive. Furfural extraction is relatively economical, but there is room for improvement here also since the furfural extracts or removes a considerable amount of useful hydrocarbons along with the metalloporphyrin complexes.

This invention has for its object to provide improved procedure for removing metalloporphyrin complexes of the volatile type (type I) from distillate fractions of crude petroleum which contain metalloporphy-rin complexes. A still further object is to provide improved procedure for removing type I metalloporphyrin complexes :and especially vanadium porphyrin complexes from distilled fractions of crude petroleum. Another object is to improve the state of the art. Other objects will appear hereinafter.

These and other objects are accomplished by my invention which includes contacting a distilled fraction of crude petroleum composed of constituents boiling above about 300 F. and containing type I metalloporphyrin complexes in harmful amounts with a liquid 2-pyrrolidone compound at a temperature between about 25 and 150 C., whereby the metalloporphyrin complexes are to a large extent dissolved in the pyrrolidone compound. Thereafter the petroleum fraction is separated from the pyrrolidone compound and the extracted metalloporphyrin complexes dissolved in the pyrr-olidone are separated therefrom. The 2-pyrro1idone compound after removal of the metalloporphyrin complexes is then used for ex traction of additional petroleum distillate fraction containing metalloporphyrin complexes.

I have found that 2-pyrrolidone compounds are outstanding solvents for the extraction of type I metalloporphyrin complexes from the heavier distillate fractions of petroleum. The 2-pyrrolidone compound not only is an excellent solvent for the metallopo-rphyrin complexes, but it is essentially immiscible with petroleum hydrocarbon fractions boiling above about 300 F. Therefore the recovery of residual solvent from the extracted petroleum or raffinate is simplified. Also the 2-pyrrolidone compound is miscible with water in large proportions so that it can be readily removed from the rafiinate in a simple manner by washing with water. Furthermore, the 2-pyrrolidone compound can be easily separated from the extract by simply diluting with water as will be more fully explained below. Also the oil is improved in respect to carbon residue, sulfur and nitrogen content as Well as in the metalloporphyrin complex content. The solvent-free residues extracted from the oils in many cases are resinous pitches indicating the high selectivity power of the 2- pyrrolidone compound for deleterious substances in the distilled petroleum fraction. An outstanding advantage of 2apyrrolidone compounds over furfural is that they give a considerably higher yield of raffinate.

My invention is applicable only to distilled petroleum fractions containing metalloporphyrin complexes. Thus 2-pyrrolidone compounds are not effective for extracting type II metalloporphyrin complexes from residual hydrocarbon fractions or from petroleum fractions containing them. Type I porphyrin complexes occur in distillates of crude petroleum whereas the type II porphyrin complexes are non-volatile and therefore do not occur in distillates. My invention is applicable only to distillates boiling above about 300 C. and preferably boiling above about 420 C. Lower boiling components than 300 C., if present in substantial amounts, cause increased solubility of the Z-pyrrolidone compound in the petroleum fraction. This lessens the selectivity and other desirable characteristics. There is no upper limit to the boiling point of the fraction. In other words the crude petroleum can be cut or distilled as deeply as desired as long as a distilled fraction is obtained and as long as precautions are utilized to avoid substantial entrainment which would carry over large amounts of type II porphyrin complexes. The use of vacuum distillation is entirely satisfactory in obtaining the distilled fraction where a high boiling fraction is desired. The invention can be applied to any distilled fraction which contains a harmful amount of metalloporphyrin complexes. Ordinarily it is applied to fractions which contain at least 10 parts per million of metalloporphyrin complexes. There is no upper limit to the amount of metalloporphyrin complexes which may be present but ordinarily crudes contain less than about 50,000 parts per million of metallop'orphyrin complexes and distilled fractions thereof would contain about this amount as an upper limit. Examples of specific petroleum fractions which may be extracted in accordance with my invention are virgin gas oil, fuel oil such as a furnace oil, coker distillates and visbreaker efiiuents.

The l-pyrrolidone compound employed as an extracting solvent has the formula in which R is an hydrogen atom or an aliphatic radical containing 1 to 3 carbon atoms such as a methyl, ethyl, propyl, vinyl, etc. Specific examples of Z-pyrrolidone compounds which may be employed as solvents are 2- pyrrolidone; 2-methyl-2-pyrrolidone; N-methyl-Z-pyrrolidone; N-ethyl-Z-pyrrolidone; and N-vinyl-Q-pyrrolidone. The solvent may be used in an amount of between about .2 and 2 volumes of solvent to one volume of oil and preferably in an amount between about .25 and 1 volumes of solvent to 1 of oil. The solvent may contain up to about 1 percent water without much eifect on the extraction. However, if more than about 1 percent water is contained in the solvent the extraction of metalloporphyrins is deleteriously affected and the carbon residue of the rai'fin-ate is higher.

The 2-pyrrolidone compounds are considerably cheaper than many solvents, such as pyridine, proposed as extracting solvents for metalloporphyn'n complexes. However these pyrrolidones are somewhat more expensive than other solvents such as furfural. This difference in cost can be considerably narrowed without adverse effect on the extraction by diluting the 2-pyrrolidone compound with a less costly lower molecular Weight aliphatic alcohol, i.e. an aliphatic alcohol containing 1 to 3 carbon atoms, for example methyl, ethyl or propyl alcohol. Thus as much as 60 percent of the extracting solvent may comprise one of these cheaper lower molecular weight alcohols without materially affecting the extraction. Amounts as low as about 10 percent alcohol advantageously can be used.

The effectiveness of such mixtures is illustrated by tests I have conducted to determine the effect of dilution of 2-pyrrolidone with ethyl alcohol. The results of these tests are given in Table I. In runs 1, 2, 4, 5, 6 and 7 of Table I gas oil distilled from Tap ar-ito crude and containing 22 parts per million of vanadium was extracted with 2-pyrrolidone containing the amounts of ethyl alcoliol indicated in Table I. The Taparito gas oil used in these particular runs was found to contain entrained class II metalloporphyrin compounds and for this reason the removal of vanadium compounds was not as good as with previous experiments. In run 3 a carefully fractionated Tap arito gas oil was extracted and this fraction contained relatively little type II metalloporphyrin compounds. The extraction was carried out by contacting the gas oil with an equal volume of the solvent or mixed solvent in a batch type operation. The contacting was carried out at approximately 70 C., the mixture being agitated every five minutes for a period of one-half hour. The mixture was then allowed to settle at about 70 C. for onealf hour, the rafiinate phase was separated, its volume determined and analyzed for vanadium content.

TABLE I Raflinate, percent Run Charge percent Wt. Rafiinate,

V,p.p.m EtOH percent on V,p.p.m. Removed Charge It will be evident from the data presented in Table I that dilution of 2-py1rolidone with as much as 50 percent ethyl alcohol had little or no effect on the percent vanadium removed. It is also evident that between 50 and 65 percent ethyl alcohol causes a marked reduction in the percent vanadium removed and that this reduction increases thereafter with increase in the amount of alco- 1101. By plotting these data in conventional fashion, it will be found that below about 60 percent ethyl alcohol can be utilized for extraction Without marked effect on the percent vanadium removal. Run 3 indicates that the percent vanadium removal is very eflicient when only type I metalloporphyrin compounds are present.

The extraction can be carried out using conventional procedure for contacting liquids with an immiscible solvent for extraction of components from the liquid. Thus it is entirely feasible, especially for small scale operations to utilize a batch contacting procedure, the distilled petroleum fraction and the Z-pyrrolidone solvent simply being agitated or stirred thoroughly and then permitted to stratify to form an upper hydrocarbon layer and a lower 2-pyrrolidone compound layer containing the extracted porphy-rin impurities. I prefer, however, to utilize the well known countercurrent contacting expedient since this enables continuous operation and gives more efficient extraction and efficient separation of the solvent from the rafiinate. In accordance with this procedure the 2- pyrrolidone compound is introduced into the upper portion of the countercurrent contacting equipment and the distilled petroleum fraction containing porphyrin complexes is introduced into the bottom of the counter-current contacting equipment. The equipment may contain any number of mixing bafiles or plates and during the downward flow of the solvent through the equipment and the upward flow of the hydrocarbon through the equipment, efiicient contacting and extraction take place. The raffinate is removed from the upper part of the countercurrent extraction column While the solvent containing the extract is removed from the bottom of the column. One satisfactory form of countercurrent contacting equipment is a Scheibel multi-stage extractor, manufactured by York Company, Inc., and described in Chemical Engineering Progress, vol. 44, pages 68l-690 and 77l-782 (1948). The extraction is carried out at a temperature which is between about 25 and C. It is advantageous to utilize as low a temperature as possible, but it is necessary that both the hydrocarbon being extracted and the solvent be in liquid phase.

After the solvent layer is separated from the hydrocarbon layer, it is advantageous to remove the residual solvent from the rafiinate and this can be accomplished in a simple manner by Washing the raffinate with water. One to three parts water to one part of raflinate will generally be found satisfactory. Between about .2 and 1 parts of Water to 1 part rafiinate are advantageously used. The raffinate, after water washing, is clear and requires no further treatment. Where recovery of traces of solvent is not important and where the presence of traces of solvent in the rafiinate has no deleterious effect, the removal of residual solvent from the raffinate will not be necessary. The water Washing, when it is employed, can be carried out at ambient temperature or at any temperature within the range employed for the extraction so long as it is below the boiling point of water under the conditions utilized.

The solvent must be separated from the extract for reuse. This may be carried out in any desired fashion. One satisfactory method is to distill the extract phase to obtain the 2 pyrrolidone compound as a distillate. However, an advantage of using a 2-pyrrolidone compound as an extracting solvent is that it can be separated from the extract phase with ease by simply diluting the extract phase with water. This forms a Water layer containing the Z-pyrrolidone compound and an upper hydrocarbon layer comprising the extracted material including metalloporphyrin complexes, sulfur and nitrogen compounds, etc. The Water layer is then separated and subjected to distillation to remove the added Water and obtain the Z-pyrrolidone compound as a heavier distillate fraction or as an undistilled residue. This Z-pyrrolidone compound is then reused in the process. It is advantageous to add to this water-2-pyrrolidone mixture prior to distillation the Water-pyrrolidone mixture obtained from the water washing of the raffinate as described above. This enables recovery of the pyrrolidone in both mixtures by a single distillation. When a mixture of alcohol and 2- pyrrolidone is used as an extracting solvent, both components will go into the water phase and may be recovered by distillation. Between about .3 and 3 parts of Water to 1 part of extract phase may be employed. In general I prefer to employ between about .5 and 1 part of water to 1 part of extract phase. The temperature of mixing of the Water with the extract phase must be below the boiling point of water and ordinarily will be at about ambient temperature. Any temperature Within the range mentioned above for the extraction with the 2-pyrrolidone compound may be used so long as it is below the boiling point of water under the conditions used.

Example Taparito gas oil having the characteristics given in column 1, Table II, was extracted with Z-pyrrolidone in a Scheibel countercurrent contacting column of the type mentioned above. The proportions of extracting solvent and gas oil at temperatures of extraction and the mixing speed are given in Table II. The rafiinate was Washed with 0.3 volume Water/volume rafiinate and the yields and vanadium contents of the various raffinates are given in Table II. The extracts were in each case diluted with 1.0 volume of water per volume of extract and the extract layer thereafter was separated from the aqueous layer. The yield of extract is given in Table II. To serve as a comparison, the same Taparito gas oil was extracted with furfural in the same Scheibel column under approximately the same conditions as indicated in Table II. The rafiinate extracts were both steam distilled to remove residual furfural. The results of these extractions with furfural are given in columns 2, 3 and 6 of Table II.

Comparison of column 2 with column 5 of Table II shows that 2-pyrrolidone very efiectively reduces the vanadium content of the gas oil to a value which is below that which is harmful to a cracking catalyst. At the same time the 2-pyyrolidone gave a 4 percent higher yield of rafiinate than furfural. In addition to this ad vantage, the recovery of solvent is considerably simplified as discussed above. Comparison of column 3 with column 4 illustrates the fact that with approximately half the volume of 2-pyrrolidone, the vanadium content is greatly reduced and the volume of raflinate is still about 4 percent higher than with furfural. Comparison of columns 6 and 7 shows that with low speed stirring and with approximately the same amount of solvent, a 4 percent higher yield of rafiinate is obtained with Z-pyrrolidone at the same metal removal level.

moving extracted metallopor-phyrin complexes from the 2-pyrrolidone compound-alcohol mixture and reusing the 2-pyrrolidone compound for further extraction of said petroleum distillate fraction containing metalloporphyrin complexes.

2. The process for treating a dis-tilled fraction of crude petroleum substantially composed of constitutents boiling above about 420 C. and containing type I vanadiumporphyrin complexes in amounts of above about 10 parts per million to remove type I vanadium-porphyrin complexes which process comprises in combination contacting said distilled fraction with a mixture containing 2-pyrrolidone and ethyl alcohol, said mixture containing between about 10 and percent ethyl alcohol, at a temperature between about 25 and 150 C., separating the extracted petroleum hydrocarbon from the 2-p-yr1'olidonealcohol mixture, removing extracted vanadium-porphyrin complexes from the 2-pyrrolidone-alcohol mixture and reusing the 2-pyrrolidone for further extraction of said petroleum distillate fraction containing vanadium-porphyrin complexes.

3. The process for treating a distilled fraction of crude petroleum substantially composed of constituents boiling above about 420 C. and containing type I vanadiumporphyrin complexes in amounts above about 10 parts per million to remove type I vanadium porphyrin complexes which process comprises in combination contacting said distilled fraction with a mixture of 10 to 60 percent ethyl alcohol and to 40 percent 2-pyrrolidone at a temperature at which the components are in liquid phase, separating the raflinate petroleum hydrocarbon from the alcohol-Z-pyrrolidone mixture, washing the raflinate petroleum hydrocarbon phase with Water to form a first water solution of 2-pyrrolidone, adding water to the separated alcohol-Z-pyrrolidone extract phase to form two layers, removing the aqueous layer and com- TABLE II Charge High Speed Stirring Low Speed Stirring Column 1 2 3 4: 5 6 7 Solvent Furural 2-Pyrrolidoue Furfural Z-Pyrrolidone Percent Water 5 5 1 1 5 1 Temperature, C 61 83 59 60 61 56 Mix Speed, r.p.m 670 7 670 690 280 280 Solvent/Oil Ratio 0.93 0.99 0. 51 0.95 1. 04 0.98 Raflinate: 1

Yield, Wt. Percent on Charge 84. 8 83. 8 87.8 88. 9 88.8 92. 7 Gravity, API 18.4 20.7 19.1 20.6 19.7 19.6 Carbon Residue, Percent Conradson-.. 1. 34 0.98 0.58 1.03 1. 22 1.08 1. 30 Sulfur, Wt. Percent (Bomb) 2.12 1.89 1.93 2.16 1.97 2.12 2. 04 Vanadium, Spectrcgraphic analysis,

p.p.m 7 1 3 1 3 3 Selectivity 6.6 5-3 4.7 7.8 5.1 7.8 Extract: 1

Yield, Wt. Percent on Charge 15.2 16. 2 12. 2 11.1 11.2 7.3

1 Solvent-free. Percent: vanadium removed/percent oil extracted. I claim: bining it with the first water solution, subjecting the com- 1. The process for treatinga distilled traction of crude bination to distillation to recover the alcohol and 2- petroleum substantially composed of constituents boiling 0 pyrrolidone and reusing the alcohol and 2-pyrrolidone for above about 300 C. and containing type I metalloporfurther extraction of said petroleum distillate fraction phyrin complexes in amounts of above about 10 parts per containing vanadium-porphyrin complexes. million to remove type I metalloponphyrin complexes which process comprises n combinat oncontactlng said References Cited in the file of this patent distilled fraction 'Wlth a mixture of a liquid 2-pyrrolrdone 5 compound and an aliphatic alcohol containing 1 to 3 carbon atoms at a temperature between about 25 and C., separating the extracted petroleum hydrocarbon from the 2-pyrrolidone compound-alcohol mixture, re-

UNITED STATES PATENTS 2,737,538 Nelson Mar. 6, 1956 2,753,381 Nelson July 3, 1956 2,846,358 Bieber et a1. Aug. 5, 1958 

1. THE PROCESS FOR TREATING A DISTILLED FRACTION OF CRUDE PETROLEUM SUBSTANTIALLY COMPOSED OF CONSTITUENTS BOILING ABOVE ABOUT 300* C. AND CONTAINING TYPE I METALLOPORPHYRIN COMPLEXES IN AMOUNTS OF ABOVE ABOUT 10 PARTS PER MILLION TO REMOVE TYPE I METALLOPORPHYRIN COMPLEXES WHICH PROCESS COMPRISES IN COMBINATION CONTACTING SAID DISTILLED FRACTION WITH A MIXTURE OF A LIQUID 2-PYRROLIDONE COMPOUND AND AN ALIPHATIC ALCOHOL CONTAINING 1 TO 3 CARBON ATOMS AT A TEMPERATURE BETWEEN ABOUT 25* AND 150* C., SEPARATING THE EXTRACTED PETROLEUM HYDROCARBON FROM THE 2-PYRROLIDONE COMPOUND-ALCOHOL MIXTURE, REMOVING EXTRACTED METALLOPORPHYRIN COMPLEXES FROM THE 2-PYRROLIDONE COMPOUND-ALCOHOL MIXTURE AND RESUING THE 2-PYRROLIDONE COMPOUND FOR FURTHER EXTRACTION OF SAID PETROLUEM DISTILLATE FRACTION CONTAINING METALLOPORPHYRIN COMPLEXES. 